An image forming apparatus (such as a laser printer) conventionally includes a cleaning apparatus for recovering toner (developer) remaining on the surface of a belt or an image bearing member and the like. Such a cleaning apparatus is limited in capacity of a accommodating chamber for storing toner to be recovered. Accordingly, a toner detection sensor is needed in order to detect whether the accommodating chamber is filled with toner. If a full condition is detected, printing operation is inhibited or the full condition is indicated to prompt the user to replace the cleaning apparatus.
The aforementioned toner detection sensor is arranged in a center of a rear wall of the accommodating chamber to detect whether toner reaches the position. However, because toner is deposited differently depending on the content of an image to be printed and the like, the toner detection sensor may detect a toner-full condition before the toner in the accommodating chamber reaches a predetermined amount, if the toner is unevenly deposited near the center in such a configuration.
With this in mind, conventionally, there has been a configuration in which a small sensing chamber is located at a rear side of the accommodating chamber, a partition member which is opened by a toner pressure is located at an opening of the sensing chamber, and a toner detection sensor is arranged in the rear wall of the sensing chamber. According to this configuration, toner enters the sensing chamber for detection after the accommodating chamber is filled with toner, thereby improving the sensing accuracy.
However, the above configuration is inconvenient for the user since printing operation terminates without notice when the accommodating chamber is filled with toner (full condition). It is preferable to detect a near-full condition in which toner is approaching the full condition and inform the user of the near-full condition before toner reaches the full condition.
Thus, there is an need in the art for an image forming apparatus capable of sensing the full condition and the near-full condition of the cleaning apparatus with a high accuracy.